The page you requested does not exist.
`), })) ``` ### JSON Errors ```go theme={null} app.Use(errorpage.New(errorpage.Options{ 404: errorpage.JSON(map[string]string{ "error": "Resource not found", "code": "NOT_FOUND", }), })) ``` ### Custom Handler ```go theme={null} app.Use(errorpage.New(errorpage.Options{ 404: func(c *mizu.Ctx) error { // Log the 404 log.Printf("404: %s", c.Request().URL.Path) // Return custom response return c.HTML(404, custom404Page) }, })) ``` ### Catch All Errors ```go theme={null} app.Use(errorpage.New(errorpage.Options{ 400: errorHandler, 401: errorHandler, 403: errorHandler, 404: errorHandler, 500: errorHandler, })) ``` ## API Reference ### Functions ```go theme={null} // New creates error page middleware func New(opts Options) mizu.Middleware // Response helpers func File(path string) Handler func HTML(content string) Handler func JSON(data any) Handler func Template(tmpl *template.Template, data any) Handler ``` ## Technical Details ### Implementation Overview The errorpage middleware uses a response writer wrapper (`statusWriter`) to intercept HTTP status codes before they are sent to the client. This allows the middleware to: 1. **Capture Status Codes**: Wraps the response writer to track status codes without immediately sending them 2. **Conditional Rendering**: Only renders error pages for status codes >= 400 when no response body has been written 3. **Template Processing**: Uses Go's `html/template` package for rendering error pages with customizable templates 4. **Default Pages**: Provides pre-configured error pages for common HTTP error codes (400, 401, 403, 404, 405, 500, 502, 503, 504) ### Response Writer Wrapper The `statusWriter` type intercepts `WriteHeader()` calls to delay status code propagation until after determining whether a custom error page should be shown: ```go theme={null} type statusWriter struct { http.ResponseWriter status int written bool } ``` This wrapper ensures that: * Status codes are captured but not immediately sent * Error pages are only shown when the response body hasn't been written * The middleware can distinguish between different error scenarios ### Error Handling Flow 1. Request enters middleware 2. Response writer is wrapped with `statusWriter` 3. Next handler is called 4. If status code >= 400 and no body written: * Custom error handler is invoked (if configured) * Custom 404 handler is invoked for 404s (if configured) * Appropriate error page is rendered using templates 5. Response is sent to client ## Best Practices * Keep error pages simple and fast * Include navigation back to home * Log errors for monitoring * Use different pages for client vs server errors ## Testing The errorpage middleware includes comprehensive test coverage for all major functionality: | Test Case | Description | Expected Behavior | | --------------------------------------------- | ------------------------------------------------ | ---------------------------------------------------------------------------- | | `TestNew` | Tests default error page rendering | Returns 404 status and displays default "Not Found" page with error code | | `TestWithOptions_CustomPages` | Tests custom error page configuration | Renders custom title "Oops!" and message for 404 errors | | `TestWithOptions_CustomTemplate` | Tests custom HTML template | Renders error using custom template format "Error 500: ..." | | `TestWithOptions_NotFoundHandler` | Tests custom 404 handler | Returns JSON response `{"error":"not found"}` instead of HTML | | `TestWithOptions_ErrorHandler` | Tests custom error handler for all errors | Returns "Custom error handler" text for any error status | | `TestWithOptions_SuccessDoesNotShowErrorPage` | Verifies successful responses bypass error pages | Returns "success" without error page interference | | `TestNotFound` | Tests NotFound() middleware function | Returns 404 status with "Not Found" text | | `TestCustom` | Tests Custom() middleware with specific pages | Renders "Maintenance" page for 503 status | | `TestPage404` | Tests Page404 helper function | Creates page with code 404 and custom title/message | | `TestPage500` | Tests Page500 helper function | Creates page with code 500 and custom title/message | | `TestDefaultPages` | Validates all default error pages exist | Confirms default pages for codes 400, 401, 403, 404, 405, 500, 502, 503, 504 | ## Related Middlewares * [recover](/middlewares/recover) - Panic recovery * [envelope](/middlewares/envelope) - Response wrapping * [logger](/middlewares/logger) - Request logging